Recent years have witnessed practical use of a flat-panel display in various products and fields. This has led to a demand for a flat-panel display that is larger in size, achieves higher image quality, and consumes less electric power.
Under such circumstances, great attention has been drawn to an electroluminescent (hereinafter abbreviated to “EL”) display device that (i) includes an EL element which uses electroluminescence (hereinafter abbreviated to “EL”) of an organic or inorganic material and that (ii) is an all-solid-state flat-panel display which is excellent in, for example, low voltage driving, high-speed response, and self-emitting characteristic.
In order to achieve a full-color display, an EL display device includes a luminescent layer which outputs light of a desired color in correspondence with a plurality of sub-pixels constituting a pixel.
A luminescent, layer is formed as a vapor-deposited film on a film formation target substrate. Specifically, in a vapor deposition process, a fine metal mask (FMM) having high-accuracy openings is used as a vapor deposition mask, and differing vapor deposition particles are selectively vapor deposited to each region of the film formation target substrate.
According to a conventional vapor deposition method, vapor deposition particles emitted from a vapor deposition source are vapor deposited on a film formation target substrate via openings of a vapor deposition mask while the film formation target substrate and the vapor deposition mask, which has the openings, are in close contact with each other. With the arrangement, in correspondence with where the openings are located, a vapor-deposited film is formed, as a luminescent layer that emits light of a corresponding one of red, green, and blue, in each of a red sub-pixel region, a green sub-pixel region, and a blue sub-pixel region.
Note, however, that vapor deposition carried out while a film formation target substrate and a vapor deposition mask are separated from each other causes a deterioration in accuracy of a vapor deposition pattern, so that an EL display device has a lower display quality. Specifically, vapor deposition particles that enter and pass through an opening at an angle, which is smaller than a given angle, with respect to a surface of the vapor deposition mask are scattered in a region outside a green sub-pixel region that is supposed to be subjected to vapor deposition. This causes a position at which a luminescent layer is to be formed to be displaced from a position at which a film formation pattern is supposed to be located, so that a so-called film formation blur occurs. Further, part of the vapor deposition particles which are scattered in the region outside the green sub-pixel region that is supposed to be subjected to vapor deposition reach a red sub-pixel region, which is adjacent to the green sub-pixel region. This causes a luminescent layer that emits green light to be formed in the red sub-pixel region, so that color mixture occurs in the red sub-pixel region.
In order to solve such a problem, there is known a technique in which a mask containing ferromagnetic metal is used, a vapor deposition mask is attracted by a magnetic force by providing a magnet on a first side of the film formation target substrate which first side is opposite from a second side of the film formation target substrate on which second side the vapor deposition mask is provided, and vapor deposition is carried out while the film formation target substrate and the vapor deposition mask are in close contact with each other.
(a) of FIG. 15 is a plan view of a vapor deposition mask that is used in a conventional vapor deposition device, (b) of FIG. 15 is a plan view of a magnet and a vapor deposition mask that are seen from the vapor deposition mask side while being provided so as to face each other, (c) of FIG. 15 is a cross-sectional view taken along the line C-C of (b) of FIG. 15.
According to a conventional vapor deposition device, for example, a metallic mask 620 provided with a plurality of slit openings 622 (see (a) of FIG. 15) is used to cause a magnet 610 and the metallic mask 620 to face each other via a film formation target substrate (not illustrated) (see (c) of FIG. 15). This allows the film formation target substrate and the vapor deposition mask to be in close contact with each other by a magnetic force.
In this case, the magnet 610 is provided so that a surface of a single magnetic pole (in the example of FIG. 15, an S pole 611N) faces one surface of the metallic mask 620. This causes the entirety of the one surface of the metallic mask 620 to be polarized so as to be magnetized to a single magnetic pole. Specifically, the one surface of the metallic mask 620 is magnetized to an S pole, whereas the other surface of the metallic mask 620 is magnetized to an N pole.
As a result, as illustrated in (b) of FIG. 15, regions between adjacent openings 622 are magnetized to the N pole, and repulsive forces generated between the regions repel each other, so that the openings 622 are deformed. Vapor deposition carried out by use of the metallic mask 620 in which the openings 622 have been deformed causes a deterioration in accuracy of a vapor deposition pattern, so that poor light emission such as uneven light emission in a pixel or color mixed light emission occurs in an organic EL display device.
As a countermeasure against the above problem, Patent Literature 1 discloses the following. Specifically, assume that a metallic mask is brought into close contact, by a magnetic force, with a vapor deposition target substrate which is provided with an organic film, and a state of contact between the metallic mask and the vapor deposition target substrate is maintained so that vapor deposition particles are vapor deposited on the organic film. In this case, by causing an adsorbability, depending on a magnet, of the metallic mask with respect to the vapor deposition target substrate to fall within a range of 0.98 kPa to 98 kPa, a long mask pattern such as a slit can be prevented from being deformed by a magnetic force.
Patent Literatures 2 through 4 disclose that a magnet for use in a vapor deposition device is exemplified by a magnet that has a plurality of magnetic domains on its surface which is in contact with a vapor deposition target substrate, the plurality of magnetic domains being arranged so that adjacent magnetic domains thereof differ in polarity.
According to a patterning device of Patent Literature 4, a magnetized member in which magnetic domains that differ from each other in polarity are alternately arranged in plan view is used to cause a long side of an opening of a metallic mask and a long side of a magnetic domain of the magnetized member to be at substantially right angles, so that the metallic mask and the magnetized member face each other via a film formation target substrate.
With the arrangement, regions between adjacent openings include a region that is magnetized to the N pole and a region that is magnetized to the S pole. Thus, in a case where a repulsive force and an attractive force that are applied to a space between the regions are offset, it is possible to prevent a change in shape of an opening (mask strain).